PVC building materials have enjoyed considerable commercial success but suffer from a number of disadvantages. Plasticized PVC is slightly yellow in color, and it tends to become more yellow on exposure to the amounts of UV light normally occurring in interior environments. The clarity and visual appearance of a plasticized PVC wear layer and the visual appearance of a decorative layer such as a printed patterned layer through a transparent or translucent wear layer are therefore not as good as could be desired. The resistance of building materials, especially countertops and flooring, to wear, abrasion, scratching and scuffing is not as great as could be desired. Vinyl building materials are marred by exposure to heat, for example lit cigarettes. The use of vinyl building materials has been objected to on environmental grounds, both in that they contain the chlorinated polymer PVC and in that they contain volatile organic compounds as plasticizers.
Ionomer resins which are thermoplastic copolymers based on an olefin and an alpha, beta-unsaturated carboxylic acid are well-known. They are described for example in an article entitled “Ionic Polymers” in Encyclopedia of Polymer Science and Engineering, Wiley-Interscience, Volume 8 (1987), pages 393–423. Most are available commercially, in many grades, for example from Du Pont under the trademark Surlyn®. They have been used as wear resistant components of building materials as described in U.S. Pat. No. 5,728,476. Since they contain no halogen they are environmentally preferable to PVC, however they require the use of additives in order to obtain the flame retardancy required by many government regulations.
Ethylene diamine phosphate (EDAP) has been used along with many other flame retardant additives (FR) in many different polymer compositions. It has the advantage that it does not contain undesirable elements such as halogens or heavy metals. However, since EDAP can have solubility problems and processing problems at higher temperatures, it has been used combined with other flame retardant additives or syngeristic additives. Additionally, use of EDAP can lead to undesirable properties of the processed polymer such as oily surface feel and cloudiness. U.S. Pat. No. 5,137,937 describes a polymer system containing thermoplastic resins and EDAP. However, that patent only exemplifies polyolefins and acetate resins.
There is a need for polymeric systems useful for surface coverings and other building materials that exhibit flame retardancy without the use of halogens but also have wear-resistant, preferably clear, coatings. Applicants have made the surprising discovery that combining two different layers, one layer containing EDAP, and the other a layer that imparts wear-resistance, will result in a composition that will pass government flame resistancy standards for building materials.